Process for producing photographic silver images

ABSTRACT

A method is described of producing photographic colour images which comprises radiation-wise exposing a photographic silver halide element and rapidly colour developing the exposed element at a temperature of at least 30*C, by means of an aromatic primary amino colour developing agent in the presence of a colour forming coupling compound, wherein the said element comprises at least one layer of a silver halide emulsion obtined by mixing, prior to coating, with the silver halide emulsion capable of producing a visible image by the said radiation-wise exposure and subsequent development, a relatively low-speed silver chloridecontaining emulsion, the speed of which is insufficient to produce a visible image by the said exposure and development. By the addition of the non-image forming silver chloride-containing emulsion to the image-forming silver halide emulsion colour images with satisfactory contrast are obtained upon processing at elevated temperature which is of particular importance for the production of radiographic colour images.

United States Patent [191 Van Doorselaer et al.

[ PROCESS FOR PRODUCING PHOTOGRAPI-IIC SILVER IMAGES [75] Inventors: Marcel Karel Van Doorselaer,

S-Gravenwezel; Valere Frans Danckaert, Boechout; Gaston Jacob Benoy, Edegem, all of Belgium [73] Assignee: Agfa-Gevaert,N.V., Mortsel,

Belgium 22 Filed: Dec.2l, 1971 21 Appl. No.: 210,566

[30] Foreign Application Priority Data Great Britain 479/71 Jan. 5, 1971 [52] US. Cl 96/22, 96/68, 96/82, 96/100 [51] Int. Cl. G03c 5/50, G03c 7/34, G03c l/92 [58] Field of Search 96/68, 74, 48 OF, 50, 94, 96/55, 121, 103, 98, 97, 59, 82; 250/315,

3,152,907 10/1964 Godowsky 96/74 3,372,030 3/1968 Jacobson 96/55 3,545,971 12/1970 Barnes 96/63 [111 3,820,991 [4 June 28, 1974 Ditzer 96/68 Marchant.........' 96/74 Primary Examiner-Ronald H. Smith Assistant Examiner-Alfonso T. Suro Pico Attorney, Agent, or Firm-Alfred W. Breiner [5 7] ABSTRACT least 30C, by means of an aromatic primary amino colour developing agent in the presence of a colour forming coupling compound, wherein the said element comprises at least one layer of a silver halide emulsion obtined by mixing, prior to coating, with the silver halide emulsion capable of producing a visible image by the said radiation-wise exposure and subsequent development, a relatively low-speed silver chloridecontaining emulsion, the speed of which is insufficient to produce a visible image by the said exposure and development. By the addition of the non-image forming silver chloride-containing emulsion to the image' forming silver halide emulsion colour images with satisfactory contrast are obtained upon processing at elevated temperature which is of particular importance for the production of radiographic colour images.

24 Claims, No Drawings PROCESS FOR PRODUCING PHOTOGRAPHIC SILVER IMAGES The present invention relates to processes for producing photographic colour images by rapid processing at elevated temperature of exposed photographic lightsensitive silver halide colour materials.

In normal processing of exposed photographic materials the various processing steps are carried out at ambient (25C) temperature and require a relatively long time, say several minutes. Therefore, there is a general trend to enhance the speed of processing especially in the field of radiography and the graphic arts so as to obtain in a couple of minutes, e.g. 90 seconds, a dry image from an element containing a latent image, development requiring less than seconds.

Apart from special processing techniques according to which. normal processing is modified e.g. in that one or more steps are combined or one or more steps are eliminated and other steps are included as is for instance the case in the so-called stabilisation processing the speed of normal processing can be enhanced by such means as the use of higher concentrations of the processing ingredients, the use of higher temperatures, the recourse to more intense agitations and the use of development-activating substances.

Though these means are generally satisfactory for the production of black-and-white images, they are far from satisfactory for the rapid processing of exposed colour materials where dye images are formed upon colour development by reaction of colour couplers with the oxidation products of aromatic primary amino colour developing agents. Yet, colour materials are of ever increasing interest. They are used in the most divergent areas of photography where it is often highly desirable to dispose of the recorded information in a minimum of time. For instance, colour materials are now used also in the field of radiography since the use of radiographic colour recording materials makes it possible to visually retrievemore information from the recorded image than from a corresponding black-andwhite image since the latter only provides differences in brightness while a colour image offers in addition thereto differences in hue and saturation. For the formation of coloured radiographs reference may be made e.g. to the published German Patent Applications 1,942,661 filed Aug. 21, 1969 and 1,946,652 filed Sept. 15, 1969 both by Agfa-Gevaert AG, which correspond to US. Pat. applications Ser. Nos. 852,236 and 852,246. both filed Aug. 22, 1969 by Agfa-Gevaert N.V. As compared with black-and-white radiography, colour radiography has one serious drawback in that rapid processing at elevated temperature in automatic X-ray processing apparatus yields dye images of unsatisfactory quality.

In rapid processing at higher temperatures, say between C and 45C, the photographic material owing to the short development time undergoes a decrease in speed and a serious loss in gradation as compared with processing at ambient temperatures wherein development lasts several minutes. v

Various methods are known to improve the speed and contrast of silver halide emulsions the most common of which is the incorporation of various additives into the emulsion and/or the developing bath such as development accelerators and superadditive developing agents. While it is possible in this way to reach by rapid development at increased temperature the same speed as obtained by normal development at ambient temperature, the gradation, especially in the higher densities, obtainable by rapid development at increased temperature is still much lower than that obtainable at ambient temperatures and therefore images of unsatisfactory quality are obtained.

It has now been found possible to produce in photographic silver halide emulsions upon exposure and rapid colour development at elevated temperature, say at least 30C, colour images of satisfactory photographic quality, and to obtain, as compared with normal development at ambient temperature, improved speed values and the same or nearly the same values for the gradation, by admixing with the image-forming silver halide emulsion, prior to coating, a relatively lowspeed silver chloride-containing emulsion of suffi ciently low speed that no visible image is produced therein under the conditions of exposure and colour development of the image-forming silver halide emul- SlOIl.

v This is rather surprising since it is known that by rapid development at elevated temperature there is a serious loss in gradation and it could not be expected that this loss could be completely or almost completely compensated by addition of a low-speed non-image forming silver chloride containing emulsion to the image-forming silver halide emulsion, although it is known from US. Pat. No. 3,152,907 of Leopold Godowsky and Jerome J. Duane, issued Oct. 13, 1964, to improve the gradation and speed by addition of such silver chloride containing emulsion to image-forming silver halide emulsions. As a matter of fact, the gain in gradation obtained according to the procedure of the United States Patent on common longtime development at ambient temperature is much less significant than the loss in gradation caused by processing at elevated temperature.

Thus, in accordance with the invention it was found that the gradation is not or much less reduced by rapid development at increased temperature and remains in a satisfactory range when to the image-forming silver halide emulsion a very low speed non-image-forming silver chloride-containing emulsion is added. This is illustrated in the examples below. Experiments wherein the low speed silver chloride containing emulsion was coated as a separate layer underneath the imageforming silver halide emulsion layer showed that this arrangement has less effect on the gradation when rapidly processing at increased temperature and therefore is less useful.

Thus, in accordance with the present invention a method is provided of producing photographic colour images, which method comprises colour'developing in the presence of a colour coupler at a temperature of at least 30C, a photographic element comprising an exposed silver halide emulsion layer wherein the said silver halide emulsion layer is obtained by mixing prior to coating with the silver halide emulsion capable of producing a visible image by the said exposure and subsequent development, a relatively low-speed silver chloride containing emulsion, the speed of which is insufficient to produce a visible image by the said exposure and development.

The colour couplers, which upon colour develop ment couple with the oxidation products of the aromatic primary amino colour developing agent, are preferably incorporated into the photographic emulsion in a non-migratory form, but they may also be dissolved in the emulsion from the developing bath.

The speed of the silver chloride-containing emulsion is not important as long as a visible image is not formed therein upon exposure and development of the imageforming silver halide emulsion. Preferably the blue light sensitivity of the image-forming silver halide emulsion is at least 100 times the blue-light-sensitivity of the silver chloride-containing emulsion. Since lightsensitivity of the silver chloride containing emulsion is not a factor the silver chloride-containing emulsion does not require a second digestion or after ripening. The low-speed silver chloride-containing emulsion, which is washed free of excess salts, is preferably a finegrain silver chloride-containing emulsion having a particle size in the range from 50 to 500 nm.

The amount of low-speed silver chloride containing emulsion to be added to the image-forming silver halide emulsion may vary within very wide limits. Favourable results may be obtained even when the ratio of low speed silver chloride to image-forming silver halide, ex-

pressed in parts by weight of silver nitrate, is as low as 1:100. The amount to be added for obtaining optimal results is dependent on the particular effect desired, on the kind of image-forming silver halide emulsion, on the nature of the low speed silver chloride containing emulsion, etc., and can be easily determined by some simple tests known to those skilled in the art.

The low'speed emulsion may be a pure silver chloride emulsion or an emulsion of mixed silver halides comprising silver chloride for example a silver chlorobromide emulsion. Low speed silver bromide or silver bromoiodide emulsions cannot be used. lt-would appear that the aimed effect is dependent on the silver chloride content in the said low speed emulsion, which means that the amount of low speed emulsion to be added for obtaining a certain effect is generally higher as the amount of silver chloride in the said emulsion is lower. Therefore, in order to minimize the amount of low speed emulsion to be added to the image-forming silver halide emulsion, the said low speed emulsion is preferably a silver chloride emulsion for the greater part.

The image-forming silver halide emulsion is preferably a medium or high speed image-forming silver halide emulsion in which the silver halide is predominantly silver bromide for example pure silver bromide emulsions and silver bromoiodide emulsions, the iodide content of which is less than mole The image-forming silver halide emulsion may be chemically sensitized by any of the accepted procedures. The emulsions may be digested with naturally active gelatin or with small amounts of sulphur containing compounds such as allyl thiocyanate, allyl thiourea, sodium thiosulphate, etc. The image-forming emulsion may also be sensitized by means of reductors for instance tin compounds as described in the United Kingdom Patent Specification No. 789,823 filed Apr. 29, 1955 by Gevaert Photo-Producten N.V., polyamines e.g. diethyltriamine, and small amounts of noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium as described by R. Koslowsky, Z. Wiss. Phot. 46, 67-72 1951). Representative examples of noble metal compounds are ammonium chloropalladate, potassium chloroplatinate, potassium chloroaurate and potassium aurithiocyanate. Of course, the

emulsions may also be sensitized chemically by the combined use of these chemical sensitizers.

Emulsion stabilizers and antifoggants may be added to the silver halide emulsion before or after admixture of the low-speed emulsion, for instance, the known sulphinic and selenic acids or salts thereof, aliphatic, aromatic or heterocyclic mercapto compounds or disulphides, preferably comprising sulpho groups or carboxyl groups, mercury compounds for example those described in Belgian Patents 524,121 filed Nov. 7, 1953 by Kodak S.A., 677,337 filed Mar. 4, 1966, 707,386 filed Dec. 1, 1967 and 709,195 filed Jan. 11, 1968 all three by Gevaert-Agfa NV. and tetraazaindenes as described by Birr in Z. Wiss. Phot. 47, 2-58 (1952) e.g. the hydroxy tetra-azaindenes of the following general formula:

wherein:

each of R and R represents a hydrogen atom, an alkyl, an aralkyl, or an aryl group, and

R represents a hydrogen atom, an alkyl, a carboxy,

or an alkoxycarbonyl group,

such as 5-methyl-7-hydroxy-s-triazolo[ 1 ,5-

a]pyrimidine.

Other additives for example hardening agents, wetting agents, plasticizers, screening dyes and spectrally sensitizing dyes can be present in the radiationsensitive silver halide elements of the invention.

In accordance with the present invention development of the exposed photographic silver halide material occurs at temperatures of at least 30C, preferably between 35C and 45C. v

The development applied in carrying out the method of the present invention is preferably an energetic surface development. The high energy is required in order to allow the development to proceed quickly and may be obtained by properly alkalizing the developing liquid (pH 9-12), by using high-energy developing substances or a combination of developing substances, which as a consequence of their superadditive action is very energetic.

Aromatic primary amino colour developing agents for example N,N-dialkyl-p-phenylene diamines and derivatives e.g. N,N-diethyl-p-phenylene diamine, N- butyl-N-sulphobutyl-p-phenylene diamine, 2-amino-5- diethylaminotoluene hydrochloride and 4-amino-N- ethyl-N(B-methane sulphonamidoe thyl)-m-toluidine sesquisulphate monohydrate and N-hydroxyethyl-N- ethyl-p-phenylene diamine can be used together with black-and-white developing agents for example l-phenyl-3-pyrazolidinone and p-monomethylaminophenol which are known to have a superadditive'effect on colour development (see L.F.A. Mason, J1. Phot. Sci. 11 (1963) 136-139), and other p-aminophenol derivatives for example those according to French Patent Specification 1,283,420 filed February 16, 1961 b 11- ford Limited, such as 3-methyl-4-hydroxy-N,N- diethylaniline, 3-methyl-4-hydroxy-N-ethyl-NB- hydroxyethylaniline, l-methyl-6-hydroxy- 1 ,2,3,4- tetrahydroquinoline, l-B-hydroxyethyl-6-hydroxy- 1,2,3 ,4-tetrahydroquinoline, N(4-hydroxy-3 '-methylphenyl)-pyrrolidine, etc. It is also possible to use combinations of aromatic primary amino colour developing agents to obtain an increased rate of colour develop ment (see e.g. German Patent Specification 954,311 filed Dec. 5, 195 3 by Agfa AG and French Patent Specification 1,299,899 filed Sept. 8, .1961 by Agfa AG); favourable effects are for instance obtained by the use of N-ethyl-N-2-hydroxyethyl-p-phenylene diamine together with N-butyl-N-sulphobutyl-p-phenylene diamine, 2amino-5'diethylaminotoluene hydrochloride or N,N-diethyl-p-phenylene diamine hydrochloride. A superadditive colour development effect is also obtained when using together with an aromatic primary amino, colour developing agent a 'tetraalkyl pphenylene diamine derivative.

For the purpose of accelerating the development, the exposed photographic material is developed preferably in the presence of development accelerators. These development accelerators can be used either in the silver comprising in one or more silver halide emulsions colhalideemulsion or in the developing bath. They include alkylene oxide compounds ,of various types e.g. alkylene oxide condensation products or polymers as described in US. Pat. Nos. 1,970,578 of Conrad Schoeller and Max Wittwer, issued Aug. 21, 1934, 2,240,472 of Donald R. Swan, issued Apr. 29, 1941, 2,423,549 of Ralph Kingsley Blake, William Alexander Stanton and Ferdinand Schulze, issued July 8, 1947, 2,441,389 of Ralph Kingsely Blake, issued May, ll, 1948, 2,531,832 of William Alexander Stanton, issued Nov. 28, 1950, 2,533,990 of Ralph Kingsley Blake, issued Dec. 12, 1950 and in United Kingdom Patent Specifications 920,637 filed May 7, 1959, 940,051

filed Nov. l, 1961, 945,340 filed Oct. 23, 1961 and.

1,015,023 filed Dec. 24, 1962 all by Gevaert Photo- Producten NV. and 991,608 filed June 14, 1961 by Kodak Ltd. Other development accelerating compounds are onium and polyonium compounds preferably of the ammonium, phosphonium, and sulphonium type for example trialkyl sulphonium sa'ltssuch as dimethyl-n-nonyl sulphonium ptoluene sulphonate, tetra-alkyl ammonium salts such as dodecyl trimethyl ammonium p-toluene sulphonate, alkyl pyridinium and alkyl quinolinium salts such as l-m-nitrobenzyl quinolinium chloride and l-dodecyl pyridinium chloride, bisalkylene pyridinium salts such as N,N-trtramethylene bispyridinium chloride, quaternary ammonium and phosphonium polyoxyalkylene salts, especially polyoxyalkylene bispyridinium salts, examples of which can be found in US. Pat. No. 2,944,900 of Burth H. Carroll, HerbertS. Elins, James L. Graham and Charles V. Wilson, issued July 12, 1960.

The developing solutions may also comprise any of the usual additional ingredients for example sodium sulphite and hydroxylamine or derivatives thereof, hardening agents, antifoggantsfor instance benzotriazole, S-nitro-benzimidazole, 5-nitro-indazole, halides such as potassium bromide, silver halide solvents, toning and intensifying compounds, solvents for instance dimethylformamide, dimethylacetamide and N-methylpyrrolidone for chemical ingredients that are difiicult to dissolve in the preparation of the developing solutions or that tend to precipitate upon standing, etc.

The invention is of particular importance for use in the production of coloured radiographs by rapid development at elevated temperature of radiographic colour our forming coupling compounds, which upon development enter into reaction with the oxidation products of the aromatic primaryamino colour developing agents to form dye images. i

The radiographic colour elements are preferably of the type described in. United States Patent application Ser. No. 852,246 mentioned above, which corresponds to the published German Patent Application 1,946,652 mentioned above and therefore this application should be read in conjunction herewith. According to United States Patent application Ser. No. 852,246 mentioned above monochromic radiographic images are produced, optionally together with a silver image in radiographic elements, which preferably comprise a colourless support and at least one silver halide emulsion layer, each such layer containing at least one colour coupler producing by coupling with an oxidized aromatic primary amino developing agent a monochromic dye image mainly absorbing in the red and green spec tral regions. 1

When in accordance with the present invention a low-speed-silver chloride-containing emulsion is mixed in the preparation of these radiographic elements, with the radiographic silver halide emulsions itis possible to obtain upon rapid development at elevated temperature improved speed and gradation characteristics and radiographic dye images can be obtained, which have as high a gradation as obtainable upon long time development at ambient temperature of the single radiographic colour emulsions.

Thus, in accordance with the present invention it is possible to produce monochromic radiographic dye images, by means of radiographic colour materials which are equivalent to conventional radiographic black-andwhite silver halide photographic materials as far as photosensitivity, gradation and ease of rapid processing at elevated temperature are concerned. Moreover, by visual inspection of the monochromic image a larger retrievalof information originally contained in the incoming radiation pattern is provided than is possible to obtain from a black-and-white silver image produced with conventional black-and-white radiographic materials.

The monochromic radiographic dye image. preferably has its main absorption in the red region (600-700 nm) of the visible spectrum and it absorbs in the green region (500-600 nm) of the visible spectrum for at least 30 percent in respect to the red region. in other words cyan dye images with a fairly large sideabsorption in the green region and blue dye images are favoured.

For this purpose, phenol or a-naphthol type colour couplers that on colour development of the exposed silver halide with an aromatic primary amino developing agent form a quinoneimine dye mainly absorbing in the red and green and having an absorption maximum in the spectral wavelength range of 550 to 700 nm, are particularly suitable.

Phenol couplers having such properties correspond, s. t thafqllsniasss tal.tq taula;

NHRa

RiHN.

wherein:

R and R each represents a carboxylic acid acyl or sulphonic acid acyl group including said groups in substituted state, e.g. an aliphatic carboxylic acid acyl group, an aromatic carboxylic acid acyl group, an heterocyclic carboxylic acid acyl group, e.g. a 2-furoyl group or a 2-thienoyl group, an aliphatic sulphonic acid acyl group, an aromatic sulphonic acid acyl group, a sulphonyl thienyl group, an-

aryloxy-substituted aliphatic carboxylic acid acyl group, a phenyl carbamyl aliphatic carboxylic acid acyl group, or a tolyl carboxylic acid acyl group.

For such types of phenol colour couplers and their preparation reference may be made to U.S. Pat. Nos. 2,772,162 of llmari R. Salminen and Charles R. Barr, issued Nov. 27, 1956 and 3,222,176 of Jan .laeken, issued Dec. 7, 1965, and to United Kingdom Patent Specification 975,773 filed Sept. 4, 1961 by Gevaert Photo-Producten N.V.

The radiographic image-forming silver halide emulsions may comprise different types of silver halide e.g. silver chloride, silver bromide, silver chlorobromide, silver bromoiodide, and silver chlorobromoiodide. Bromide emulsions containing iodide, preferably containing less than mole of iodide, are especially useful for directly or indirectly recording penetrating radiation in the form of a monochromic image.

The radiographic colour elements preferably comprise on both sides of a transparent support e.g. a transparent resin support, a silver halide emulsion layer comprising a colour coupler for producing a monochromic dye image and a protective hydrophilic colloid layer coated thereover.

1n the formation of the silver halide emulsions and the protective colloid coatings all kinds of ingredients characteristic for the formation of radiographic elements used in the direct or indirect recording of penetrating radiation, may be employed. These ingredients include chemical and spectral sensitizers, antifoggants, stabilizers and development accelerators as described hereinbefore as well as hardening agents e.g. formaldehyde, dialdehydes, hydroxy aldehydes, mucochloric and mucobromic acid, acrolein, and glyoxal, lightscreening dyes, mordanting agents for anionic colour couplers or dyes formed therefrom, plasticizers and coating aids, e.g. dialkylsulphosuccinic acid salts such as sodium diisooctylsulphosuccinate, alkylaryl polyether sulphuric acids, alkylaryl polyether sulphonic acids, carboxyalkylated polyethylene glycol ethers or esters as described in French Patent Specification 1,537,417 filed September 18, 1967 by Agfa-Gevaert N.V. Such as iSOC H17-'C6H4(OCH2CH2)EOCH- COONa, fluorinated surfactants e.g. those described in Belgian Patent Specification 742,680 filed Decem her 5, 1969 by Gevaert-Agfa N.V. as well as the follow- S OaNB CsFt1S IN( zHt) (CH2CH20)(OC t The exposed radiographic colour elements are processed in accordance with the present invention at elevated temperature, preferably in conventional automatic processing apparatus for X-ray films in which the photographic material may be guided automatically and at a constant speed from one processing unit to the other in such a way that the processing time in each processing unit does not last longer than 1 minute at 30C.

In carrying out the method of the present invention in an automatic processing unit it is also possible to keep the photographic material motionless and to apply the successive processing liquids automatically.

Since the silver image need not be removed, the development step need not be followed by a bleaching step so that a processing as simple as that for producing black-and-white radiographs can be applied.

The following examples illustrate the present inventlon.

EXAMPLE 1 5 samples were prepared by adding each time to 157 g of a high speed silver bromoiodide emulsion (9 mole of Agl), which comprises an amount of silver halide equivalent to 26.8 g of silver nitrate and 17.8 g of gelatin, the following:

for sample 1 14.5 g of gelatin for sample 2 14.2 g of gelatin and 4.6 g of a low speed silver chloride emulsion comprising an amount of silver chloride equivalent to 0.54 g of silver nitrate and 0.29 g of gelatin so as to obtain in the mixture the same total amount of gelatin as "in sample 1 and a ratio of silver bromoiodide to silver chloride corresponding to :2 in parts by weight of silver nitrate;

for sample 3 as for sample 2 but 13 g of gelatin and 22.8 g of the same silver chloride emulsion (ratio of silver bromoiodide to silver chloride corresponding to 100:10 in parts by weight of silver nitrate);

for sample 4 as for sample 2 but 7.2 g of gelatin and 1 14 g of the same silver chloride emulsion (ratio of silver bromoiodide to silver chloride corresponding to 100250 in parts by weight of silver nitrate);

for sample 5 as for sample 2 but no gelatin and 228 g of the same silver chloride emulsion (ratio of silver bromoiodide to silver chloride corresponding to 100: 100 in parts by weight of silver nitrate).

The five samples thus contain the same amount of gelatin, the same amount of silver bromoiodide and increasing amounts of silver chloride.

The low speed silver chloride emulsion was prepared by admixing an aqueous solution of silver nitrate to an aqueous gelatin-sodium chloride solution, precipitating the gelatin emulsion with ammonium sulphate, washing and peptizing. Gelatin was then added as well as 5- methyl-7-hydroxy-s triazolo[ l,5-a]pyrimidine so that no chemical ripening occurred. The mean grain-size of the silver chloride emulsion was 220 nm.

The mixed samples were then molten by heating for 1 hour at 38Cwhereupon were added to each sample:-

91 ml of an aqueous'emulsion (latex) of a polymeric cyan-forming coupler with formula:

1 r CHr-CH til sq.m). On both sides a gelatin anti-abrasion layer of I 0.0015 mm was provided whereupon the photographic elements formed were dried.

Strips of the 5 film samples obtained were exposed to light through a wedge under identical circumstances and then colour-processed (A) at ambient temperature (C) and (B) at increased temperature (41C), as

idicated in the following table 1.

Table 1 Processing Colour- Fixing Rinsing Drying(55C) development A (20C) 4 min 45sec 4 min 4 min 2 min B (41C) 24 sec 20 sec 25 sec 20 sec The developing bath used had a pH of 10.6 and comprised per litre: 8 g of N-hydroxyethyl-N-ethyl-pphenylenediamine, 1.5 g of hydroxylamine, 4 g of anhydrous sodium sulphite, 1 g of potassium bromide and, 65 g of anhydrous potassium carbonate. Fixing occurred by means of a sodium thiosulphate fixing solution.

The coloured photographic wedge prints thus obtained were measured by means of a conventional colour densitometer provided with a red filter. The sensitometric results are listed in table 2. The log E values measured for the speed at density 0.25 above fog are given in the form of relative values, the value of 100 being given to the speed of filmsample 1 processed at ambient temperature. As gradation-values are given the slopes of the sensitometric curves between densities 0.25 above fog and 2.00 above fog.

Table 2 Sample Processing A Processing B Fog Rel. Grada- Fog ReLSpeed Grada- Speed tion tion From the above results the following can be learned:

a. The addition of the silver chloride emulsion causes an increase of the speed both by processing A(20C)' and by processingv B (41C);

b. In the case of film sample 11 where no silver chloride emulsion has been added to the silver bromoiodide emulsion there is a severe loss in gradation by processing at increased temperature (from 2.10 to 1.33) whereas in the case of film samples 2 to 5 there is practically no loss in gradations(samples 2, 4, and 5) or even an increase in gradation (sample 3).

This means that the gain in gradation by addition of the silver. chloride emulsion is less significant (from 2.10 to 2.25 2.50) when processing at ambient temperature than when processing at increased tempera ture (from 1.33 to 2.05-2.40). Thus, these results show that by rapid processing at increased temperature the same value for the gradation can be reached as by slow processing at ambient temperature, when a low speed silver chloride emulsion is admixed with the high speed silver bromoiodide emulsion.

EXAMPLE 2 Two emulsion samples were prepared by adding each time to 313 g of the same bromoiodide emulsion of example the following:

for sample 1 15.2 g of gelatin for sample 2 9.4 g of gelatin and 91.2 g of the silver chloride emulsion of example 1 so as to obtain the same total amount of gelatin as in sample 1 and a ratio of silver bromoiodide to silver chloride corresponding to 100220 in parts by weight of silver nitrate;

Both samples were molten as described in Example 1, and to each were added:

1. 15.5 g of the magenta-forming colour coupler of the formula:

dissolved in a mixture of 100 ml of water, 31 ml of ethylalcohol and 15.5 ml of 2N sodium hydroxide.

2. An aqueous acetic acid solution in the amount necessary to neutralize the foregoing alkaline solution.

Table 3 Sample Processing A Processing B Fog Rel. Grada- Fog ReLSpeed Grada- Speed tion tion From the above results the following can be learned:

a. The addition of the silver chloride emulsion causes an increase of the speed both at 20C (from 100 to l 14) and 41C (from 95 to 141) the speed increase being, however, markedly higher at 41C.

12. In the case of sample 1 (without AgCl) the speed obtained by rapid processing at increased temperature is practically the same as that obtained by slow processing at ambient temperature whereas by addition of the silver chloride emulsion (sample 2) the speed obtained by rapid processing at increased temperature is higher than that obtained by slow processing at ambient temperature.

c. By rapid processing at increased temperature there is a loss in gradation as compared with slow processing at ambient temperature. This loss, however, is markedly higher in the case of sample 1 (from 2.15 to 1.15 i.e. 46.4 percent) than in the case of sample 2 (from 2.95 to 2.49 i.e. 15.5 percent). In other words the increase in gradation by addition of a low-speed silver chloride emulsion is markedly higher when processing at increased temperature (from 1.15 to 2.49 i.e. 107 percent) than when processing at ambient temperature (from 2.15 to 2.95 i.e. 37 percent).

a. By addition of a silver chloride emulsion it is possible to reach by rapid processing at increased temperature a higher gradation value than obtained at ambient temperature without addition of a slow-speed silver chloride emulsion.

EXAMPLE 3 Five film samples were prepared in the same way as described in example 1 with the only'difference that the silver bromoiodide emulsion used now contained 5 mole of silver iodide instead of 9 mole Exposure and processing of the film samples occurred as described in example 1 with the difference that, owing to the greater developability of the high speed emulsion with lower silver iodide content, the development time was reduced to 3 min. 15 sec. at 20C (processing A) and to 18 sec. at 41C (processing B).

The sensitometric results attained are listed in the following Table 4.

Table 4 Sample Processing A Processing B Fog Rel. Grada- Fog Rel.Speed Grada- Speed tion tion The above results once again show that by addition of the low-speed silver chloride emulsion a substantial increase in speed and gradation can be obtained by rapid processing at increased temperature; this increase markedly exceeds that obtained by normal processing at ambient temperature. By addition of the low speed silver chloride emulsion to the high speed silver bromoiodide emulsion it is possible to reach in substantially less time higher speed values and approximately the same gradation as obtainable by normal processing without addition of silver chlo r i de emulsion.

EXAMPLE 4 Five emulsion samples were prepared in a similar way as described in example 1, with the difference that the low speed silver chloride emulsion was added to the high speed silver bromoiodide emulsion in the form of 'ide:

sample 1 only silver bromoiodide sample 2 an amount of silver bromoiodide equivalent to 100 parts of silver'nitrate and an amount of silver chloride equivalent to 1.9 part of silver nitrate sample 3 an amount of silver bromoiodide equivalent to 100 parts of silver nitrate and an amount of silver chloride equivalent to 9.5 parts of silver nitrate.

sample 4 an amount of silver bromoiodide equivalent to 100 parts of silver nitrate and an amount of silver chloride equivalent to 19 parts of silver nitrate.

sample 5 an amount of silver bromoiodide equivalent to 100 parts of silver nitrate and an amount of silver chloride equivalent to 47.5 parts of silver nitrate.

Exposure and processing of the film samples occurred as described in example 1 with the difference that the development time at 41C (processing B) was now 27 seconds.

The following sensitometric results were obtained.

Sample Processing A Processing B Fog Rel. Grada- Fog Rel.Speed Grada- Speed tion tion dissolved in 130 ml of 2N sodium hydroxide,

EXAMPLE 5 2 emulsion samples were prepared by adding each time to 202 g of a high speed silver bromoiodide emulsion (5 mole of Agl), which comprises an amount of silver halide equivalent to 25.9 g of silver nitrate and 25.9 gof gelatin, the following:

for sample 1 514.2 g of gelatin for sample 2: 7.2 g of gelatin and 117 g of a silve chloride emulsion as described in example 1 so as to obtain in the mixture the same total amount of gelatin as in sample 1 and a ratio of silver bromoiodide to silver chloride corresponding to 100250 in parts by weight of silver nitrate. Both samples were molten as described in example 1, and to each were added:

mule;

0 NHC mn 2. an aqueous acetic acid solution in an amount necessary to neutralize the foregoing alkaline solution, and

3. a stabilizer, wetting agent and hardener.

After digestion for 3 hours the emulsion samples were coated as described in example 1 and the corresponding film samples 1 and 2 were exposed and processed as described in example 1, with the difference that the development time was reduced to 3 min. sec. at C (processing A) and to 18 sec. at 41C (processing B). a

The sensitometric results attained from which the same conclusions can be drawn as in the foregoing examples, are listed in the following table 5.

l. a solution of 13 g of the colour coupler of the for- Table 5 Sample Processing A Processing B Fog Rel. Grada- Fog ReLSpeed Grada- Speed tion tion We claim:

1. A method for producing a color image with photographic color materials wherein a latent image in a radiographically exposed photographic element comprising at least one photographic silver halide emulsion layer is color developed at a temperature of at least 30C. by means of an aromatic primary amino colordeveloping agent in the presence of a color-forming coupling compound, including the sequential steps of (a) mixing a silver halide emulsion which will produce a visible image upon radiographic exposure and subsequent development atsaid elevated temperature with a relatively lowspeed silver chloride-containing emulsion, the speed of which is insufficient to produce a visible image upon radiographic exposure and subsequent development at said elevated temperature; (b) using said mixed emulsion (a) to form a photographic element; (c) radiographically exposing said element (b); and (d) developing photographic element (c) at a temperature of at least 30C. with a color developer containing an aromatic primary amino color-developing agent and a color-forming coupler compound.

2. Method according to claim 1, wherein the said silver chloride-containing emulsion is a silver chlorideo silver chlorobromide emulsion.

3. Method according to claim 1, wherein the said silver chloride-containing emulsion has a particle size between 50 and 500 nm.

. 4. Method according to claim 1, wherein the blue light sensitivity of the image-forming silver halide emulsion is at least 100 times the bluelight-sensitivity of the non-image forming silver chloride containing emulsion.

5. Method according to claim 1, wherein the imageforming silver halide emulsion is a medium or high speed silver bromide or silver bromoiodide emulsion.

6. Method according to claim 1, wherein the ratio of low-speed silver chloride to image-forming silver halide expressed in parts by weight of silver nitrate is at least 1:100.

7. Method according to claim 1, wherein the said colour forming coupling compound is present in the said silver halide emulsionlayer.

8. Method according to claim 1, wherein development occurs at a temperature comprised between 35 and 45C and lasts less than 1 min.

9. Method according to claim 11, wherein said silver halide emulsion layer contains at least one color coupler which upon development by coupling with an oxidized aromatic primary amino color developing agent produces a monochromic dye image mainly absorbing in the red and green spectral regions.

10. Method according to claim 9, wherein the said dye in said image has its main absorption in the red region (600-700 nm) of the visible spectrum and absorbs in the green region (500-600 nm) of the visible spectrum for at least 30 percent in respect of the red region.

11. Method according to claim 9, wherein the said colour coupler is a phenol or a-naphthol type colour coupler.

12. Method according to claim 10, wherein the said colour coupler is a colour coupler corresponding to the formula:

NHR1

RgHN

wherein:

each of R, and R is a carboxylic or sulphonic acid a y p- 13. Method according to claim 9, wherein said element has a transparent support and at both sides of the support a said silver halide emulsion layer.

14. A radiographic silver halide element for the production of radiographic monochromic dye images ineluding a support and at least one radiation-sensitive silver-halide emulsion layer having increased speed and being capable of producing upon exposure and rapid color development at elevated temperature in the presence of a color coupler a monochromic dye image of increased contrast mainly absorbing in the green and red spectral regions, wherein the said silver halide emulsion in said emulsion layer is formed from a mixture of a silver halide emulsion capable of producing a visible image by the above said exposure and subsequent rapid development and a relatively low speed silver chloride-containing emulsion the speed of which is insufficient to produce a visible image by the said exposure and development.

15. A radiographic element according to claim 14, wherein the colour coupler is present in the said emulsion layer.

16. A radiographic element according to claim 14, wherein the said silver chloride-containing emulsion is a silver chloride or silver chlorobromide emulsion.

17. A radiographic element according to claim 14,

wherein the said silverchloride-containing emulsion has a particle size between 50 and 500 nm.

18. A radiographic element according to claim 14, wherein the blue-light sensitivity of the image-forming silver halide emulsion is at least times the blue-light sensitivity of the non-image forming silver chloride containing emulsion.

19. A radiographic elementaccording to claim 14, wherein the image-forming silver halide emulsion is a medium or high speed silver bromide or silver bromoiodide emulsion. p

20. A radiographic element according to claim 14, wherein the ratio of low-speed silver chloride to imageforming silver halide expressed in parts by weight of silver nitrate is at least 1:100.

21. A radiographic element according to claim 14, wherein the said dye in said image has its main absorption in the red region (600-700 nm) of the visible spectrum and absorbs in the green region (500-600 nm) of the visible spectrum for at least 30 percent in respect of the red region.

22. a radiographic'element according to claim 14, wherein the said colour coupler is a phenol or a-naphthol type colour coupler.

23. A radiographic element according to claim 22, wherein the said colour coupler is a colour coupler corresponding to the formula:

NHR

said silver halide emulsion layer. 

2. Method according to claim 1, wherein the said silver chloride-containing emulsion is a silver chloride or silver chlorobromide emulsion.
 3. Method according to claim 1, wherein the said silver chloride-containing emulsion has a particle size between 50 and 500 nm.
 4. Method according to claim 1, wherein the blue-light sensitivity of the image-forming silver halide emulsion is at least 100 times the bluelight sensitivity of the non-image forming silver chloride containing emulsion.
 5. Method according to claim 1, wherein the image-forming silver halide emulsion is a medium or high speed silver bromide or silver bromoiodide emulsion.
 6. Method according to claim 1, wherein the ratio of low-speed silver chloride to image-forming silver halide expressed in parts by weight of siLver nitrate is at least 1:100.
 7. Method according to claim 1, wherein the said colour forming coupling compound is present in the said silver halide emulsion layer.
 8. Method according to claim 1, wherein development occurs at a temperature comprised between 35* and 45*C and lasts less than 1 min.
 9. Method according to claim 1, wherein said silver halide emulsion layer contains at least one color coupler which upon development by coupling with an oxidized aromatic primary amino color developing agent produces a monochromic dye image mainly absorbing in the red and green spectral regions.
 10. Method according to claim 9, wherein the said dye in said image has its main absorption in the red region (600-700 nm) of the visible spectrum and absorbs in the green region (500-600 nm) of the visible spectrum for at least 30 percent in respect of the red region.
 11. Method according to claim 9, wherein the said colour coupler is a phenol or Alpha -naphthol type colour coupler.
 12. Method according to claim 10, wherein the said colour coupler is a colour coupler corresponding to the formula:
 13. Method according to claim 9, wherein said element has a transparent support and at both sides of the support a said silver halide emulsion layer.
 14. A radiographic silver halide element for the production of radiographic monochromic dye images including a support and at least one radiation-sensitive silver halide emulsion layer having increased speed and being capable of producing upon exposure and rapid color development at elevated temperature in the presence of a color coupler a monochromic dye image of increased contrast mainly absorbing in the green and red spectral regions, wherein the said silver halide emulsion in said emulsion layer is formed from a mixture of a silver halide emulsion capable of producing a visible image by the above said exposure and subsequent rapid development and a relatively low speed silver chloride-containing emulsion the speed of which is insufficient to produce a visible image by the said exposure and development.
 15. A radiographic element according to claim 14, wherein the colour coupler is present in the said emulsion layer.
 16. A radiographic element according to claim 14, wherein the said silver chloride-containing emulsion is a silver chloride or silver chlorobromide emulsion.
 17. A radiographic element according to claim 14, wherein the said silver chloride-containing emulsion has a particle size between 50 and 500 nm.
 18. A radiographic element according to claim 14, wherein the blue-light sensitivity of the image-forming silver halide emulsion is at least 100 times the blue-light sensitivity of the non-image forming silver chloride containing emulsion.
 19. A radiographic element according to claim 14, wherein the image-forming silver halide emulsion is a medium or high speed silver bromide or silver bromoiodide emulsion.
 20. A radiographic element according to claim 14, wherein the ratio of low-speed silver chloride to image-forming silver halide expressed in parts by weight of silver nitrate is at least 1:100.
 21. A radiographic element according to claim 14, wherein the said dye in said image has its main absorption in the red region (600-700 nm) of the visible spectrum and absorbs in the green region (500-600 nm) of the visible spectrum for at least 30 percent in respect of the red region.
 22. a radiographic element according to claim 14, wherein the said colour coupler is a phenol or Alpha -naphthol type colour coupler.
 23. A radiographic element according to claim 22, wherein the said colour coupler is a colour coupler corresponding to the formula:
 24. A radiogRaphic element according to claim 14, wherein the photographic silver halide element has a transparent support and at both sides of the support a said silver halide emulsion layer. 